The present invention relates to a method and apparatus for extracting fluid from a slurry and more particularly to such a method and apparatus for extracting fluid such as juice, finished to a relatively high degree, from a slurry such as an initial juice including substantial solids. It is particularly contemplated that the method and apparatus be employed for use with slurries in the form of initial juices obtained from fruits including citrus fruits and vegetables. However, it will be apparent that the method and apparatus of the invention may be employed in connection with slurries formed from almost any product wherein it is desirable to obtain a relatively finished fluid from a slurry including substantial solids.
In the production of juices from various fruits and vegetables, it has been common practice to first obtain an initial or raw juice which may contain substantial amounts of various solids such as rag, pulp from juice sacs, pectinous material, seeds, etc. Such initial juices have been obtained by various juice extraction machines. Typical examples of such juice extraction machines are disclosed, for example, in U.S. Pat. Nos. 2,631,625 and 4,170,935. In the first noted reference, a machine is disclosed in which fruit or the like is cut in half and transferred into conveyor cups. Rotary reamers are then driven into engagement with the conveyor cups to extract juice from the fruit.
Similarly, U.S. Pat. No. 4,170,935 discloses a machine wherein fruit or the like is cut in half and conducted through gradually convergent paths to flatten the halves and express or extract the pulpy juice therefrom. These machines are effective as primary extractors for obtaining initial or raw juice. However, it is desired to remove solid components from the juice to provide a so-called finished juice.
Typical commercial machines for effecting the conversion of initial juice to finished juice, or removal of components from other types of slurries, have been characterized as either so-called screw-type or paddle-type finishers. In the screw-type finishers, the initial juice or slurry is introduced into a stationary screen. A rotary screw is mounted within the screen and designed to have a fairly close tolerance fit with the screen. Generally, such screw-type finishers are of two different types. In one type the screen and the outside diameter of the screw are tapered with the smallest diameter at the discharge end. The root of the screw is tapered and the pitch of the flights varies so that the cross sectional area between the flights decreases at the discharge end. In other screw-type finishers, the screen and the outside diameter of the screw are cylindrical. The root of the screw may be conical with the large diameter at the discharge end, or the root of the screw may be cylindrical.
In both of the above screw-type finishers, pulp escape valve means are provided at the discharge ends and are either spring or air loaded. As the fluid or juice component from the initial juice or slurry is removed during passage through the screen, substantial solids build up at the discharge end and it is sometimes necessary to apply somewhat excessive air pressure against the valve means to assure removal of additional juice through the built-up solids. Such action has been found to be detrimental to juice quality.
In paddle-type finishers the slurry is introduced into a stationary screen of conical or cylindrical shape. Helical blades are rigidly mounted for rotation within the screen and extend through the length of the screen. These blades function somewhat as a screw to convey the slurry along the screen and force components of the slurry through the screen. The clearance between the elongate blades and the screen must be adjusted in consideration of the components to be forced through the screen from the slurry. This, of course, requires loosening and tightening of the blade fasteners and careful adjustment of the elongate blades, which results in shut-down time.
Accordingly, there has been found to remain a need for an improved finishing method and apparatus capable of overcoming one or more problems of the type outlined above and thereby resulting in production of a finished juice or the like of high quality. It will be apparent that similar advantages can be realized in connection with many other slurries in addition to the specific juices as described above.